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Patterns and Functions of Grooming Behavior among the Common Indian Langur Monkey James J. McKenna

For many primate species grooming is a predomin- These data suggest, particularly with respect to the ant and socially important behavior pattern diverse question of functions, that while grooming no doubt both in the form it can take and the social situations serves both social and hygienic functions, it does so in a within which it is initiated. While not the only behavior context apparently dictated -by social needs. It is con- that often cuts across different age and sex classes to cluded that social grooming among langur monkeys is promote cohesion, the tremendous amount of time highly integrated into almost all aspects of group life and energy invested by some species in this activity and, while not a reliable behavioral index to status suggests that as a bond-building mechanism social differentials between group members, it is important grooming has played an auxiliary if not complemen- in assessing role complexes. tary role in the evolution of primate sociality. Among primates social grooming is thought by in- Materials and Methods vestigators to provide useful information on many dif- The study group was housed in a dome-shaped ferent aspects of group life. Grooming data has been mesh enclosure approximately 35 feet high by 45 feet used to measure developmental processes in the in diameter. Starting from the enclosure floor six dif- mother-infant relationship (Hinde 1974, Kaufman ferent levels ofsitting bars and platforms, interspersed and Rosenblum 1969), to document the growing net- every three to five feet, allowed proper social and work of attachments and subgroup formations within spatial refuge. An L-shaped mesh partition support- and among different primate groups (Simonds 1973, ing plywood sitting platforms was situated in the 1974; Furuya 1957; Kummer 1968), and as an exam- center of the enclosure. ple of parental investment (Trivers 1974, Hrdy 1976). According to Jay's (1965) field data, the population While Sade (1965) and Lindberg (1973) demonstrated structure included an adult male (about ten years of how grooming patterns reinforce social relationships age with extracted canines and musculature fully de- and, in some cases, regulate behavior, Chance and veloped); eight adult females (all at least silx years of Jolly (1970) suggested that within private societies the age, primiparous or multiparous); four immature direction of grooming can be used as one criterion to juvenile females (all between the ages of two and four delineate "attention structures" and to assess the de- years of age); four immaturejuvenile males (with mus- gree of social centrality of leader individuals around culature not fully developed and incompletely which others are organized. More recently, Boese erupted canines); and, finally, two dependent infants (1976) used data collected on preferred grooming less than eight months old. clusters to propose that West African baboons (Papio To collect data on the form, frequencies, and dura- papio) exhibit harem units based upon sexual but not tions of behavioral patterns for group members three social exclusivity. different sampling techniques were utilized: focal be- Although an impressive number of works dealing havior samples, focal animal samples, and behavior primarily with the social functions of grooming exist, spot checks. A focal behavior sample involved a fifteen there is not unanimous agreement that grooming be- minute observation period wherein all grooming ac- havior has been interpreted and dealt with correctly, tivities were recorded and notation was made ofwhich nor that its function has been entirely understood. animal initiated the grooming interaction, which other Alexander (1974) argues that not enough attention animal received it, its context, and what part of the has been given to the disease-controlling functions of anatomy was groomed. During a focal animal sample grooming, particularly since grooming may have orig- all behavior exhibited by and toward one individual inally functioned only as a parasite-controlling (the focal animal) during a fifteen minute observation mechanism and not as an accomodation to group liv- period was recorded. The duration of the behavior, ing. To varying degrees Alexander's position receives the actor, the receiver and the participants were noted. support from Hutchins and Barash (1976) and Free- Behavior spot checks involved a random scan and land (1976) who strongly argue that a much closer look periodic survey of the momentary activities of each at the relationship between disease pressures and so- individual at the time of observation (see Altmann cial behavior is warranted. 1974). Combining the three sampling procedures a This paper examines the forms, the contexts, and total of 1500 observation hours were completed. the functions of social grooming behavior among the Tabulation of the data followed the procedure used common Indian langur money (Presbytis entellus). by Lindberg (1973), in which a grooming bout was 4

considered to be any paired occurrence of grooming 60% (n= 1146) classified as relaxed social grooming, involving a recognizable actor and receiver not inter- 4% took the form ofmutual grooming (animal A and B rupted by a third animal or by a major relocation of groom each other simultaneously); 53% involved one of the participants. Reciprocal grooming (animal allo-grooming (animal A grooms animal B); 42% in- A grooms B, then, animal B grooms A) was considered volved reciprocal grooming (animal A grooms animal as two different bouts. If three or more animals B, then, animal B grooms animal A); and, finally, in groomed simultaneously (animal A grooms animal B less than 1% of the relaxed social grooming total the while animal C grooms A), each grooming dyad was form of grooming was unclear, since observation scored separately. If more than ten seconds passed began after the animals had initiated the interaction. between bouts, or it a grooming sequence was termi- Aggressive behavior preceded 63% of tension- nated but begun again after an individual invited a reducing grooming bouts (667 or 35% of all social partner to resume grooming, then this was scored as a grooming bouts observed). Ventral-ventral embracing second grooming bout even though the participants was the second most frequent behavior to precede had previously groomed during the sampling period. tension-reducing grooming with 22% of the total. Sexual solicitations, social mountings, and social pre- Forms of Grooming senting were roughly equal in eliciting grooming re- Although the contexts were varied, three types of sponses (2.5%, 1%, and 4.2% respectively). grooming were recognized for captive Hanuman lan- The third and least frequently observed form of gurs: 1) relaxed social grooming, 2) tension-reducing grooming among captive langurs was self-grooming. grooming, and 3) self-grooming (see table 1). Groom- This form of solitary skin care occurred in 4% of the ing interactions involving more than one animal and total number of grooming behaviors observed. Al- not accompanied by aggressive or tense vocalizations, though spatial and, therefore, social isolation often postures, and/or facial expressions (grimaces) were preceded self-grooming, it was certainly not the only scored as bouts ofrelaxed social grooming. In contrast, condition in which it was initiated. Self-grooming any bout preceded by an embrace, a social present, often occurred between reciprocal grooming sessions aggressive behavior, a social or sexual mount, or a and/or following or preceding allo-grooming by either sexual solicitation involving tense vocalizations and/or one of the participants. facial expressions was scored as a tension-reducing groom. Finally, self-grooming was scored when an in- Frequency and Distribution of Grooming Patterns dividual licked or picked through its own skin, hair, or by Age and Sex Class teeth. Figure 1 shows the percentages by which age and sex classes acted and received Grooming Behavior social grooming (relaxed and tension-reducing grooming combined). Based SOCIAL (96%) SELF (4%) upon 94 fifteen-minute on each of the ____ samples adults RELAXED (60%) TENSION-REDUCING (35%) and immatures (excluding the neonates) and 399 focal

la 0 _ behavior hours (1,596 fifteen-minutes observation periods) I found that during any one sample period an average of 3.6 individuals could be found either as - a 0q a

time in grooming, males invest little and receive much Ad' A¶? (see Figure 2). 60 I S4 Not only did adult females initiate social grooming 0 more frequently and for longer periods of time, but ; 50 their grooming networks were much more extensive. 0 Inasmuch as 37% of their grooming was directed to- cd ".~440 ward the immature males and females and 23% to- 0 ward the adult male, the adult females clearly directed Xl 30 ew grooming across age and sex classes in opposite social 20 directions. Particularly for the immature males, the social grooming by the adult females seemed to have 8 10 an integrating effect. Because the adult male C.) main- tained exclusive sexual (copulatory) rights to the adult females, the immature males as potential sexual com- Acts Groom petitors had ambiguous and precarious social posi- Receives Groom tions. However, the adult male threatened the imma- ture males only when they were sexually solicited by Figure 1. Percentage contribution by age and sex class adult females but not when they were groomed by to acting and receiving social grooming. them. Whatever peripheralizing effect the adult male may have had on the immature males, these socio- less grooming than any of the immature females and sexual proscriptions appeared counteracted by the far less than one of the immature males, who topped grooming activities initiated by the adult females. her grooming scores by over 58 initiated grooming Without disruption to the society, the immature males bouts. This kind of individual variation holds true for were drawn into the social nucleus of the group to comparisons between other individuals of different establish tactile relationships with adult females. age and sex classes as well. Therefore, it is important to realize that general interclass distinctions are often different from the behavioral records of individuals. 0 Age and sex class membership promotes relative but 0 ~ 5 not absolute interclass differences.

00 Duration versus Frequency of Grooming I V? Although frequency counts reveal what behaviors 32 are more likely to be exhibited by members of various U Id' subgroups of the society, the figures, if taken alone, ¢ w are inadequate or, worse, misleading. For example, HZ~: the data reveal that quantitative differences of groom- I I ing interactions are sometimes less than dramatic (e.g. the adult male compared with some of the adult mean females); however, by examining the quality of groom- median ing as defined by the length oftime one animal actually Figure 2. Mean and median duration of initiated social grooms another, more meaningful differences ap- grooming per animal per class. pear. Here an extreme example can be made between the adult females and the adult male. As described previously, the adult male was involved in over 10% of Grooming Invitations and Methods the observed social grooming and during these in- The most common social grooming solicitation oc- teractions he was the recipient far more frequently curred in relaxed social settings and was scored when than he was the actor. The grooming data are even an actor, moving into proximity of another (within 12 more skewed in favor of the adult male when the inches), attempted either by watching or hand man- duration of his grooming activities is considered. ipulation to establish visual or passive tactile contact While the mean duration of social grooming by the with a potential groomer. After succeeding and while adult females of the adult male is 4.6 minutes, the in close proximity, the actor stretched its ventrum usu- mean duration of his reciprocal grooming of the adult ally in front ofthe receiver and while scratching its own females was only 23 seconds (as timed by a stop watch). ventrum, the actor (inviter) looked away. Although In general, both the frequency and quality (as defined over 33% of the relaxed social grooming bouts were by duration) of social grooming initiated by adult and preceded by such a grooming solicitation, there were immature females is substantially different from that many variations of this sequence. Occasionally, an exhibited by males. While females invest a great deal of actor established eye contact but then immediately 6

looked away from the receiver while scratching its gression has ceased and that non-aggressive behaviors ventrum or an actor stretched and presented its ven- may be resumed between them. trum without scratching. An alternative grooming in- vitation was leaning forward in front of a potential The Relationship Between Grooming and Aggression groomer, sometimes establishing tactile contact, or To better assesss the functional relationship bet- lying stretched out on the belly (ventrally) either di- ween grooming and aggression among captive langur rectly in front of the receiver or lying over part of the monkeys, a correlation coefficient which measures the receiver's body, such as a leg. The draping of an arm degree or extent of a linear relationship between the over another animal while simultaneously avoiding two behaviors was computed. By using 500 fifteen- eye contact could also elicit social grooming bouts and minute focal behavior samples for aggression and 500 preceded 6% of them. In many instances of social fifteen-minute focal behavior samples for grooming, grooming no invitation was apparent. However, with the proportion of times each individual received ag- respect to social grooming bouts in which no grooming gression and acted in grooming was determined first. invitation was observed (23%), the groomer often had After computing paired scores for each animal in the approached the receiver from a different area of the group (X=proportion of times animal A received ag- enclosure. It might be that in these contexts grooming gression, and Y=proportion of times animal A acted acted as an appeasment mechanism that allowed an grooming) I entered the data into a Pearson-r correla- animal to relocate socially with respect to another by tion matrix. The resulting (r) was interpreted in the reducing the possibility that its presence would elicit an following way: if (r) was negative, it indicated that as aggressive response. grooming increased aggression received decreased With respect to tension-reducing grooming it is ex- and vice-versa; if (r) was 0, no linear relationship ceedingly difficult to discuss what constitutes an invita- existed between the two behaviors; and, finally, if (r) tion because in only 3.8% of such bouts was there a was positive, grooming increased as aggression in- grooming solicitation performed in the manner de- creased and vice-versa. Testing to determine if the (r) scribed above. Reference to context is essential because value was significant (p. <.01), a t-value was deter- tension-reducing grooming is fundamentally a part of mined and compared with the tabular (t) value with a series of behavioral events in which either the n-2 degrees of freedom. groomer or groomee has been involved. Tension- The correlation proved positive (r= +4.68 with a reducing grooming typically followed aggression, a t=2.94). In other words, within the specified confi- social or sexual mount, presenting, and/or ventral- dence intervals it can be expected that when grooming ventral embracing (Table 1). It may be interspersed increases between individuals so will aggression. It is between any sequence of these behavior patterns or interesting to find that, if taken at face value, the any combination of them. commonly held assumption that grooming solidifies After approaching and tagging the adult male in a relationships, strengthens social bonds and, as a result, sequence interpreted as a confirmation of their age decreases the amount of aggression directed toward and sex class roles with respect to each other, a young those who perform it, has proved questionable. Yet, immature male may immediately run to a peer group especially in this instance interpreting a cause-and- member and, while vocalizing and grimacing, be effect relationship is extremely risky. Clearly, the groomed by him. Alternatively, the peer group statistics reveal the importance ofconsidering not sim- member might mount him first, then, groom him. ply the numbers, but considering the contexts from It is not always the receiver of aggression that does which the numbers were obtained. The question to be the grooming. Following an embrace with an aggres- asked is the following. In light of the statistics, which sor the recipient of the aggression may turn away and, suggest otherwise, can it still be assumed that among while grunting and grimacing, be groomed by him. the common hanuman langur grooming has a positive, These behavioral sequences suggest the possibility that or tension-reducing effect on the group at large? in such contexts the mount, the embrace and similar One must consider several factors. The form of ag- actions communicate a desire to be groomed (possibly gression directed by individuals is not made explicit by for reassurance). Tension and conflict situations which the correlation. Most aggression was neither tactile nor vary greatly in their intensities and form clearly com- serious but instead it involved facial, bounce, or hand plicate the discussion ofgrooming invitations and their threats. So too, aggression was often directed in a functions. Indeed, the possibility exists that particular positive way as, for example, to stop others from fight- behaviors such as grooming have multiple functions ing, to quell factionalism, and to protect infants from and, depending upon the specific situation and the inept substitute caretakers. The adult females per- specific individuals, multiple meanings. In one context formed most of these aggressive policing roles, and the recipient of aggression may groom to appease the since they also were involved in more grooming in- aggressor and to prevent the aggression from continu- teractions than any other age and sex class the chances ing while in another context the aggressor may groom were increased that grooming and aggressive scores the victim, thereby reassuring the recipient that ag- would compute linearly. But the most important part 7 of the question remains, and that is whether grooming Anatomical Area %of Sample Groomed behavior is a mechanism that can promote peace by Back (Dorsum) 22.2% -4 Area 11.6% reducing aggressive levels. It is here that an analysis of Caudal .1 Underarms (Axilla) 3.6% context shows that in over half of all the aggressive e Shoulders 3.2% interactions (both tactile and nontactile), grooming Top of Head 9.3% immediately followed and was initiated by the receiver Face-Teeth 5.5% of that aggression. That social grooming functions not T=55.4% only to promote bonds and relationships, but also to Hands 3.1% circumvent continued aggression by one animal to Forearms 8.6% another is suggested by the data. Tension-reducing Ventral-Thoracic Area 11.6% grooming may not always be successful in preventing Posterior-Ventral-Abdominal Area 6.0% aggression but for most members of a society its effi- Hindlimbs 4.0% Tail (Medial, Distal) 11.3% cacy is impressive. While grooming typically follows T= 44.6% aggression it does not usually precede it (McKenna 1975). Table 2. -Anatomical foci ofsocial grooming (n= 1,662 receivers of social grooming) Anatomical Focus of Social and Self Grooming Hanuman langurs groomed all parts of the body. Relaxed Tension- From a sample of 693 social grooming bouts the Social Reducing analysis indicates that those anatomical regions out of Grooming Grooming sight or reach of a recipient of grooming were more Ventral-Ventral Orientation 44% 23% frequently groomed by another animal than were ac- (animals face each other) areas. Whereas 55% ofthe sample involved the cessible Ventral-Dorsal Orientation 41% 69% grooming of areas designated inaccessible to the reci- (receiver of grooming turns pient of grooming (see Table 2), 45% of the social away from actor) grooming involved accessible areas. Whether or not social grooming of inaccessible regions promotes Unclear Body Orientation 15% 8% hygiene by removing ectoparasites, thereby decreas- ing possibility of disease, cannot be quantitatively de- Table 3. Percent of relaxed and tension-reducing grooming bouts in monstrated but such may be the case. It is important, which different body orientations were assumed by grooming dyads however, to consider the context of the initiated bout, (an actor and receiver). for the data reveal that the context often determines which part ofthe body will be groomed. For example, a Anatomical Area % Groomed ventral-dorsal orientation was assumed by a groomer Forearms 29.7 and aggressor, respectively in over 75% of the re- Tails 36.1 Genitals 8.0 sponses initiated by an attacked animal immediately Chest (Thoracic Area) 5.0 following attack. Eye contact was either broken al- Lower Abdomen 4.2 together, or at least avoided in such incidents, and the Medial Thighs and Hindlimbs 8.0 social grooming of an inaccessible region of the ag- Hands 3.0 6.0 gressor's body was initiated by the attacked animal. Feet While this behavior may prove hygienically beneficial Table 4. Anatomical focus of self-grooming (n=55) in the long run, how it comes about can be explained in terms of the immediate social rewards for each of the participants. A review of the self-grooming data (Table 4) reveals During relaxed social grooming there is, likewise, a that during nonsocial grooming sessions animals pre- tendency to avoid body orientations which require sus- ferred to groom their tails more often than any other tained and direct eye contact i.e, a ventral-ventral part of their bodies (36% of the sample), while groom- dyadic orientation. However, as Table 3 reveals, the ing ofthe forearm followed second in frequency (29%; proportion of times animals are oriented away from Figure 3). The fact that tails were most often groomed each other in a ventral-dorsal position is far less than in during solitary grooming sessions is understandable the case during tension-reducing grooming (41 % ver- since they were the most vulnerable part of the body. sus 69% of the total). At least among captive langur Cuts and lacerations of the distal and medial aspects of monkeys it can be speculated that the grooming of the tail were frequently sustained. The animals often inaccessible regions of the body appears to be regu- caught their tails on parts of the enclosure. Genital lated not strictly by hygienic or health needs but by self-grooming was most commonly observed among social strategies having immediate social consequences the immature males (6%of the 8% total). It was com- such as suppressing further factionalism and inter- mon for males to sustain an erection during these animal aggression. grooming periods but none were seen to ejaculate. 8

Figure 3. An adult female grooms herself while simultaneously nursing her infant and sitting- in-contact with her three year old adolescent daughter. Discussion plimentary relationship, Weber contends that a In Weber's (1973) discussion of'tactile communica- "symmetrical" relationship can be said to exist bet- tion amnong free-rangiing langurs grooming behavior ween them (Weber 1973:483). is described as one of nine "meaningful combinations While Weber may be correct in suggesting that of communication sequences." While discussing the actor and receiver roles in particular interactional fun1ctions of tactile behaviors including grooming he settings may (at times) rieflect dominance and subor- states, " . in these patterns social needs of bodily dinance and, thus, are complimentary (his defini- corntact are articulated and satisfied; they are social tion), the data collected here suggest that his explana- expressions of accepting and being accepted" (Weber tion cannot accurately be applied to all grooming 1973:481). Similar to the findings here but not al- interactioins between the adult male and females, nor together in agreement with them Weber found that to many of the other social interactions that occur reciprocal gi-ooming was much more common in between them. As was shown earlier, adult and im- "same-sex" subgroups than it was in subgroups con- mature males frequently groomed adult females and taiming both sexes and that one-sided grooming by individual females responded differentially to the adult females of adult males was typical. He proposed grooming solicitations of' the adult male. In the event that this one-sidedness of grooming activities occur- that an adult female ignores a grooming invitation ring between the adults is explained by the fact that and refuses to groom the adult male (which fre- " . . . the interactions between adult males and females quently occurred), usiIng Weber's definition of com- in heterosexual groups are always complimentary" plimentarity the adult female behaves in a dominant (Weber 1973:483). Complimentary interactions are (i.e. passive) role with respect to the adult male who, defined in terms of status differentials between the in turn, behaves in the subordinant (i.e. actor) role. interacting participants. Accordingly, the adult male The point is that in reference to dyadic situations is always the receiver (i.e. dominant) in grooming complimentarity is more accurately defined in terms interactions and, consequently, does not reciprocate. of what the animals are actually doing with respect to As actors in grooming interactions the females are each other rather than in terms of status differentials always the suboidinants. If reciprocal grooming oc- because as a behavioral index the dominance/ curs between any two animals, rather than a com- subordinance characterization is often unreliable, 9 particularly when describing the grooming relation- Probably few investigators will deny that cleaning ships between male and female adult langurs. So too, the fur can be extremely important particularly when females spend much more time grooming each other animals spend much of their time foraging in litter, than they spend grooming adult males so it can be swampy areas, or dead wood (Hladik 1975). However, expected that between them much more reciproca- researchers might argue about the utility of deciding tion will take place. Furthermore, female-female which function (social or hygienic) was important bonds established and maintained through reciprocal first, especially since natural selection does not oper- grooming may be more closely tied to the other social ate in a vacuum, nor upon one specific behavioral roles females perform such as infant caretaking, sol- strategy at a time. Instead, natural selection works iciting sexual behavior, and policing activities rather simultaneously on all the behavioral subsystems than a reflection of a general social position they which, to greater and lesser degrees, influence the occupy with respect to the males (see McKenna 1975). species ability to successfully reproduce. My guess is It is important, therefore, to view grooming behavior that structural and physiological adaptations rather not in terms of status differentials but in terms of how than social ones are more likely to have been initially this behavior reflects role complexes and interrelated selected for in order to control diseases brought about behavior sets that relatively but not absolutely dif- by ecto-parasites especially since internal parasites ferentiate age groups, sex groups, and age and sex which cannot be removed by grooming are just as groups combined. By doing so the question of func- serious a problem. But it seems useless to speculate in tion is best approached because it forces a more com- this way since in certain areas parasites and disease prehensive evaluation of the behavior as it relates to can be as much an ecological limiting factor as the other social and physical needs. availability and distribution of food. Consequently, From this more flexible position the positions of grooming must be subsumed into a broader context Alexander (1974) and Freeland (1976) can be consi- which includes reference to such behavioral subsys- dered. Alexander suggests that in the beginning tems as feeding and ranging patterns, sexual be- grooming behavior controlled parasites and only later haviors, rearing practices, predator and incest avoi- assumed significant social functions. He states, dance, defense strategies and locomotion, all of 'That parasite-controlling behavior should acquire a which gradually emerged in response to environmen- social role only illustrates the effects of group living tal pressures. upon the way selection changes behavior ... Such What is needed to test Alexander's contentions and relationships between selection and different social the sweeping hypothesis proposed by Freeland is a functions and effects must be understood if social cross-specific comparison of sympatric species that organization is to be clarified or traced from the be- must cope with similar pathogens and disease pres- ginning" (Alexander 1974: 331). Freeland takes Ale- sures. In areas of intense parasite infestations groom- xander several steps further when he hypothesizes ing ought to be elaborated, at least according to Ale- that troop compositions, infant-caretaking behaviors, xander (1974). If not, a determination of what sexual behaviors and inter-group relationships are mechanisms are important in controlling them selected specifically to reduce the acquisition of new should be made. Experimental manipulations of pathogens and to "minimize the pathogenicity ofdis- groups (relocations of groups from areas with diffe- ease" the individuals of a group might already harbor rent parasite pressures) could reveal the processes by (Freeland 1976: 12). which such adaptations are made and, perhaps, the While the data on langurs presented here can role of grooming as a practical vehicle for parasite neither verify nor refute these authors' contentions, control. Only after acquiring such data can we accu- they can be useful in assessing the overall feasibility rately assess the etiologies of grooming. of their arguments. For example, it was shown that langurs tended to groom inaccessible regions of the Summary and Conclusions body rather than accessible regions. This information An intensive study of captive Indian langurs (Pre- and the observations made by Curtin (1975) that solit- sbytis entellus) revealed that grooming behavior was ary male langurs during the wet season suffered from exhibited more frequently and for greater periods of leach infestation lends support for the hygienic ar- time than was any other social behavior. Whereas the gument. However, it was also shown that ventral- frequency by which adult females initiated social dorsal body orientations which expose inaccessible grooming was much greater than that amount in- areas to others for grooming were governed not only itiated by any other age and sex class, there are impor- by the immediate social context (relaxed or tense) but tant intraclass variations and when individual also by the nature ofthe relationship existing between grooming records are considered, age and sex class the participants. This point is mentioned to dispel distinctions with respect to grooming become less any interpretation which evokes a genetical link bet- absolute. Characteristically, females groomed for ween grooming behavior and part of the body longer periods of time and their grooming networks groomed. were much more extensive. Cutting across age and I ()

Figures 4 and 5. Relaxed and reciprocal social grooming is exhibited between these two adult females. In the top photo adult female A (on the right) grooms adult female B (on the left) in a ventral-ventral orientation. In the bottom photo Animal A has turned away from animal B and the grooming roles of the participants are reversed and demonstrate a ventral-dorsal orienta- tliOIi. 11

sex class boundaries the grooming activities of adult attending to it and providing tactile enjoyment while females may function to enhance group integration the recipient ofaggression and the actor ofthe groom- especially since their grooming activities include ing manipulates an aggression-receiving situation immature males whose positions in the group are into a peaceful one. socially tenuous. With the present data in mind some tentative con- Social grooming solicitations and the contexts in clusions can be offered. Among Hanuman langurs which grooming occurred were tremendously di- social grooming is intimately fused with almost all verse. While the majority of grooming bouts were aspects of social life and can be used to manipulate described as relaxed, tension-reducing grooming social situations and to establish important social al- which was recognized when one or both ofthe groom- liances. The argument that grooming originally ing participants exhibited tense facial expressions or evolved as a parasite-controlling mechanism appears vocalizations occurred after aggressive interactions, simplistic and ignores the fact that natural selection before and after social mounts, during sexual and works not upon one behavior but on complexes of infant-caretaking activities, following social presents behavior and makes continuous compromises on the and after ventral-ventral embracing. In addition, it efficacy of each adaptive strategy. The "complimen- was found that although grooming invitations or sol- tarity" of grooming behavior as defined by Weber icitations were not often a part of a tension-reducing wherein active/passive, dominant/subordinant roles sequence as they were a part of the relaxed social are ascribed to adult male and female langurs is, grooming bouts, in the majority of cases it was the likewise, unsatisfactory particularly since status dif- receiver of aggression who acted the grooming while ferentials are so fluid in langur society. No doubt the aggressor turned away and received it. The rela- social grooming performs dualistic social and tionship between grooming and aggression proved to hygienic functions but given the social base from be an interesting one since a positive correlation coef- which colobines evolved it may prove unwise to ficient was computed. As the frequency of grooming separate the two, especially since both immediate and increased between individuals so did aggression or long terms benefits are mutually derived. vice-versa. The computation of this statistic reveals the value of considering context since rarely (if at all) did aggression follow grooming behavior between participants. In most instances aggression preceded it. Hence, grooming seemed to promote the restora- tion of peaceful relationships between individuals and the cessation of hostilities. As an appeasement mechanism the grooming behavior of captive langur monkeys cannot be underestimated. With respect to the strong statements put forth by Freeland (1976), Alexander (1974) and Hutchins and Barash (1976) on the disease-controlling functions of grooming behavior these data can neither prove, nor disprove their contentions. It was, however, stressed that among langurs the part of the anatomy exposed by one animal to another is primarily determined by the nature of the interaction preceding the grooming bout. Inaccessible areas of the body were groomed most often after aggressive encounters. More specifi- cally, ventral-ventral grooming sessions, i.e. groom- ing interactions that involved the animals facing each other in which eye-contact was sustained, occurred most often during relaxed social grooming bouts. During tense grooming encounters ventral-dorsal body orientations permitting the avoidance of eye- contact between grooming dyads were more com- mon. These facts are relevant to understanding the circumstances in which inaccessible parts ofthe body are sometimes groomed. While this grooming may function in the long run to decrease disease poten- tials, the actions of both participants (actor and re- ceiver) provide immediate social rewards; the actor of the aggression is appeased by the attacked animal 1 2

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